Limiters are rather special and can also be rather dangerous for you sound, they act like a compressor, but as the name suggests they stop anything going above a threshold, but why would you use one.
Where there is a high Dynamic Range, it's very useful, Dynamic Range is the distance between the LOUDEST and quietest parts of the track, and you can see this from the waveform, if there are huge peaks and troughs, then it usually has a high DR, some rock has a very small DR and the waveform just looks like a solid line.
Small DR's tend to be boring to the listener, so good mixing is essential to achieve this, part of this is to limit some of the louder instruments, so they don't go over a certain level, "Why don't you just turn it down on the fader?" You could do that, but you might just make it quieter, what we are after is to keep it well in the mix, and hear it, this is where a compressor comes in, anything over a threshold will be compressed and the volume not reduced, a limiter can be more vicious, it stops anything going over the threshold, nowadays, limiters can be very clever, I use the Waves L3 maximiser limiters on many of my tracks and it just gives it some oomph, and brings it alive. Place it on the last plugin slot on your master buss and hear the difference, use it sparingly, when applied to the Master buss, it's applied to the whole song.